The advantages of molecular-based memory devices include nanoscale size, low voltage operation and multiple-state properties. Multiple-state behavior can be built into the molecular structure via molecular design and chemical synthesis. For example, the porphyrin molecule shown in FIG. 1a exhibits three states: neutral, monopositive, and dipositive [D. T. Gryko et al., J. Org. Chem., 64 (1999)]. More elaborate molecular structures have been devised that afford up to seven positively charged states [K. Schweikart, et al., J. S. J. Mater. Chem., 12 (2002); see also U.S. Pat. Nos. 6,128,214; 6,208,533; 6,272,038; and 6,212,093].
A hybrid semiconcutor/molecular approach, where molecules are integrated with silicon devices, can provide a bridge between CMOS-only and future molecular-only technologies [K. M. Roth et al., J. Vac. Sci. Technol. B, 18 (2000); C. P. Collier et al., Science, 285 (1999); S. K. Coulter, J. Vac. Sci. Technol. A, 18 (2000); K. M. Roth et al., J. Am. Chem. Soc., 125 (2003)]. However, little has been suggested in connection with such devices, and there is a need for new approaches to hybrid molecular memory devices.